Generally, a linear stepping motor is a motor in which a rotor rotates at a predetermined angle to allow a lead screw to linearly and reciprocally move. The linear stepping motor is featured by the fact that the number of an input pulse and a rotation angle of a motor are proportionate to accurately control the rotation angle, such that the linear stepping motor is widely used that needs a precise control.
The linear stepping motor is largely utilized in the fields of NC (numerical control) machines, industrial robots, and office automation machines such as printers and copiers, and is particularly used as an actuator adjusting an illumination angle of a head light of an automobile.
FIG. 1 is a cross-sectional view illustrating an example of a linear stepping motor according to prior art.
Referring to FIG. 1, the conventional linear stepping motor includes a housing 1, a control box 3 mounted outside of the housing 1, a stator 5 installed inside the housing 1, a rotor 7 rotatively installed inside the stator 5 to be rotated by the electromagnetic force, and a lead screw 9 linearly and movably installed inside the rotor 7 to linearly move in association with the rotating movement of the rotor 7.
The stator 5 includes a pair of tooth yokes 50, and first and second coil bobbins 52,54 wound by a coil 56 and arrange in parallel outside of the tooth yokes 50.
The rotor 7 includes a magnet 70 rotatively mounted inside the tooth yoke 50 at a predetermined gap, and an arm screw 72 installed to rotate along with the magnet 70 inside the magnet 70 and formed therein with a female screw 72 formed with female screw threads 72a. 
Furthermore, the lead screw 9 is formed at a periphery thereof with a male screw threads 9a meshed with the female screw threads 72a of the female screw 72 to linearly and reciprocally move in response to the rotation of the female screw 72.
FIG. 2 is a schematic view of essential parts illustrating a bearing installation structure of a linear stepping motor according to prior art.
Referring to FIG. 2, the linear stepping motor is configured in such a manner that a plate cover 11 is welded to one side of a housing 1, where the plate cover 11 is coupled with a mounting plate 13. The mounting plate 13 is formed with an installation groove 13a inside of which is installed with a bearing 15 for rotatively supporting one side end of the lead screw 9. At this time, the bearing 15 is blocked by a lateral wall 1a of the housing 1 to be prevented from being disengaged.
However, the conventional linear stepping motor suffers from a disadvantage in that it must satisfy a condition in which a diameter d2 of a central hole 1b formed at the center of the housing 1 is smaller than an outer diameter d1 of the bearing 15 to prevent the bearing 15 from disengaging (d1>d2). As a result, the diameter of the central hole 1b must be designed based on the outer diameter of the bearing 15 to limit the designing condition of the housing 1.
In association therewith, the size of the magnet 70 positioned inside a tooth 1c bent from the central hole 1b must be determined by the diameter of the central hole 1b, whereby the size of the magnet 70 is also restricted based on the limiting condition in which the diameter of the central hole 1b cannot be arbitrarily enlarged or reduced.
Furthermore, in order for the housing 1 to precisely apply pressure to the bearing 15, a coupling accuracy of a mounting plate 13, a plate cover 11 and the housing 1 must be very important, and in order to satisfy the coupling accuracy of these elements, a manufacturing cost is inevitably increased to meet the meticulous design conditions and manufacturing processes. If the meticulous design conditions are not met, vibration and noise are inevitably generated by the axial motion of the bearing 15 to become causes of defect of the product.